1. Field of the Invention
This invention relates to electronic circuit technology, and more particularly, to a differential signal driven direct-current (DC) voltage generating device which is designed for integration to a PLL (phase-locked loop) or a DLL (delay-locked loop) circuit system for generating an output of a DC voltage in response to an input of a differential signal, such as a phase-difference signal.
2. Description of Related Art
In PLL (phase-locked loop) and DLL (delay-locked loop) circuitry, the charge pump is an essential circuit component capable of being driven by a pair of phase-difference signals (which respectively indicate the lagging or leading of the output frequency generated by the PLL or DLL circuitry with respect to a reference frequency) and responsively generating an output of a DC voltage whose amplitude is proportional to the phase difference between the output frequency and the reference frequency. Fundamentally, the lagging of the output frequency against the reference frequency will result in a negative phase-difference signal which is presented as a pump-up enable signal (UP) to the charge pump; whereas the leading of the output frequency will result in a positive phase-difference signal which is presented as a pump-down enable signal (DN) to the charge pump. The output of the charge pump is a DC voltage which is subsequently used as a control voltage for a VCO (voltage-controlled oscillation) circuit for adjusting its output frequency to match in phase with the reference frequency.
Theoretically, the output frequency range of a PLL-VCO circuit is proportional to the amplitude range of the input control voltage, i.e., the output DC voltage range of the charge pump. Accordingly, if we want to increase the PLL-VCO output frequency range, it can be achieved by increasing the output voltage range of the charge pump.
In practice, however, traditional charge pump circuits are only capable of offering a limited output voltage range; and therefore, the VCO circuits are also only capable of offering a limited range of output frequencies in proportion to the charge pump voltages.
In view of the foregoing problem, there exists therefore a need in the electronics industry for a new circuit technology that allows PLL/DLL circuit systems to offer a wider range of output frequencies.